1. Field of the Invention
The present invention relates to an optical communication, and more particularly, a photonic cross-connector system connecting paths of wavelength division multiplexing (WDM) signals, a WDM system using the photonic cross-connector system, and an optical communication network based on the WDM system.
2. Description of the Related Art
Recent information communication user environments have been suddenly ubiquitous. Thus, information society-based networks have been developed from existing fixed forms to variable forms. In addition, inventions of network node apparatuses have been increased to simply install, operate, and maintain network apparatuses. These apparatuses may be realized through a minimization of an optical-to-electric-to-optical transformation, efficiency of routing and wavelength allocation, optical switching and branching/coupling of channels of a control system.
FIG. 1 is schematic view illustrating a wavelength division multiplexing (WDM) optical communication network. Referring to FIG. 1, the WDM optical communication network may include a plurality of networks having different physical characteristics such as a used wavelength and a modulation method, i.e., a network A 10 and a network B 20. A node used inside a network having the same physical characteristic, i.e., a photonic cross-connector system, requires a switching function of transmitting signals input from different ports to a desired output port. When a signal of a network having a different physical characteristic, i.e., the network A 10, is connected to the network B 20, a node at a boundary between the networks A and B 10 and 20 requires a wavelength transformation, an optical reproduction, a change of a modulation method, etc. A node 8 shown in FIG. 1 must perform such a function.
There is increased a demand for a multicasting method by which a signal generated in a departure is simultaneously transmitted to a plurality of destinations with the arrival of an Internet protocol television (IP-TV), a teleconference, a virtual private network (VPN), etc. In the multicasting method, a plurality of signals are not generated in a departure and not transmitted to a plurality of destinations. However, a signal is generated and then transmitted a predetermined distance through a common path and diverges from a divergence node to each destination. Thus, traffic of the optical communication network can be reduced.
For example, when a signal generated by a node 1 of the network A 10 is to be simultaneously transmitted to nodes 6 and 7, the signal is first transmitted through nodes 1, 4, and 5 and then copied and diverged from the node 5 into the nodes 6 and 7. Since an existing optical communication network through which an IP signal is transmitted does not provide a switching function, such multicasting is performed by an electrical IP router. Thus, a minimization of an optical-to-electric-to-optical transformation and efficiency of routing and wavelength allocation cannot be realized.
There is suggested a photonic cross-connector system which divides signals input through an optical fiber according to each wavelength, transmits the same wavelength of various wavelengths divided from different optical fibers to a switch, switches the wavelength according to each path, and transmits the wavelength. However, such a photonic cross-connector system does not perform an optical multicasting function and a modulation method conversion function. There is suggested a photonic cross-connector system which realizes a switch switching the same wavelengths to different paths to support a multicasting function with a split and delivery (SaD) including a plurality of optical couplers, a gate optical switch, and a 1:N optical switch. However, the photonic cross-connector system uses optical couplers, wherein the number of optical couplers is equal to the number of wavelengths. Thus, loss is very large, and a large number of optical switches must be used. Also, like the previously described photonic cross-connector system, the present photonic cross-connector system does not provide a function of multicasting to different wavelengths and a function of transforming a modulation method.
There is suggested a photonic cross-connector system which divides an input signal to two paths using a coupler, connects the one of the two paths to a drop path and the other one to a transmission path, and disallows the signal to be transmitted to the transmission path using a wavelength blocker or simultaneously transmits the signal to the drop and transmission paths so as to perform a multicasting function. However, the photonic cross-connector system limits each of input and output ports and does not provide a function of multicasting to different wavelengths and a function of transforming a modulation method.
An optical signal is frequently deteriorated during its transmission due to a chromatic dispersion of an optical fiber, a polarization mode dispersion, noise of an optical amplifier, etc. Thus, each node, i.e., a photonic cross-connector system, requires a function of regenerating a signal, transforming the signal into a clear signal, and transmitting the clear signal to a destination port.